The Zika virus (ZIKV) of the flaviviridae family of viruses poses a significant threat to the health of newborn infants and young children. ZIKV infection predominantly affects the development of the nervous system and its neurotopism has been well-established. In September 2016, ZIKV was linked to sensorineural hearing loss in newborn infants that were prenatally exposed, but essentially nothing is known about where the developmental pathologies lie in the auditory pathway. Reports of abnormal otoacoustic emissions in ZIKV-exposed infants suggest that at least some of the sensorineural defects may originate within the cochlea, the auditory organ of the inner ear. This study will focus on correlating the timing of ZIKV exposure at embryonic and perinatal stages to the types of inner ear cells that become infected, using two animal models (chicken and mice). Preliminary data show that ZIKV can infect the cochlea, in particular the sensory domain, the stria vascularis (tegmentum vasculosum in the chicken cochlea) and the auditory ganglion. The proposed studies will involve delivery of ZIKV directly to the embryonic inner ear and the cochlea to assess cellular tropism and otic pathogenesis associated with ZIKV. Aim 1 will determine the cellular tropism and timing of ZIKV infection in ovo by direction injection of virus into the chicken otocyst from embryonic day (E) 3?5. Virus distribution, cell proliferation, apoptosis, and gene expression related to innate immune responses will be assayed several days after infection. Aim 2 will determine the cellular tropism and timing of ZIKV infection in vitro in embryonic (E12.5, E15.5) and neonatal (postnatal day 1) mouse cochlea cultures. Genetic labeling of hair cells, supporting cells, or intermediate cells of the stria vascularis will aid in following the fates of these cell types for up to 6 days in culture. Virus distribution, cell proliferation, apoptosis, hair cell ultrastructure, and hair cell mechanotransduction will be evaluated several days after ZIKV exposure. Antibody blocking experiments will be used to explore the role of the periotic mesenchyme as a direct target of ZIKV. These studies should aid in understanding how ZIKV infection of the developing sensory periphery might contribute to sensorineural hearing loss in human infants.